fix PR5262.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84810 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 9147a99..60e2d7f 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -9274,13 +9274,43 @@
return Changed ? &SI : 0;
}
-/// isDefinedInBB - Return true if the value is an instruction defined in the
-/// specified basicblock.
-static bool isDefinedInBB(const Value *V, const BasicBlock *BB) {
- const Instruction *I = dyn_cast<Instruction>(V);
- return I != 0 && I->getParent() == BB;
-}
+/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
+/// PHI node (but the two may be in different blocks). See if the true/false
+/// values (V) are live in all of the predecessor blocks of the PHI. For
+/// example, cases like this cannot be mapped:
+///
+/// X = phi [ C1, BB1], [C2, BB2]
+/// Y = add
+/// Z = select X, Y, 0
+///
+/// because Y is not live in BB1/BB2.
+///
+static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
+ const SelectInst &SI) {
+ // If the value is a non-instruction value like a constant or argument, it
+ // can always be mapped.
+ const Instruction *I = dyn_cast<Instruction>(V);
+ if (I == 0) return true;
+
+ // If V is a PHI node defined in the same block as the condition PHI, we can
+ // map the arguments.
+ const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
+
+ if (const PHINode *VP = dyn_cast<PHINode>(I))
+ if (VP->getParent() == CondPHI->getParent())
+ return true;
+
+ // Otherwise, if the PHI and select are defined in the same block and if V is
+ // defined in a different block, then we can transform it.
+ if (SI.getParent() == CondPHI->getParent() &&
+ I->getParent() != CondPHI->getParent())
+ return true;
+
+ // Otherwise we have a 'hard' case and we can't tell without doing more
+ // detailed dominator based analysis, punt.
+ return false;
+}
Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
Value *CondVal = SI.getCondition();
@@ -9493,16 +9523,13 @@
return FoldI;
}
- // See if we can fold the select into a phi node. The true/false values have
- // to be live in the predecessor blocks. If they are instructions in SI's
- // block, we can't map to the predecessor.
- if (isa<PHINode>(SI.getCondition()) &&
- (!isDefinedInBB(SI.getTrueValue(), SI.getParent()) ||
- isa<PHINode>(SI.getTrueValue())) &&
- (!isDefinedInBB(SI.getFalseValue(), SI.getParent()) ||
- isa<PHINode>(SI.getFalseValue())))
- if (Instruction *NV = FoldOpIntoPhi(SI))
- return NV;
+ // See if we can fold the select into a phi node if the condition is a select.
+ if (isa<PHINode>(SI.getCondition()))
+ // The true/false values have to be live in the PHI predecessor's blocks.
+ if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
+ CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
+ if (Instruction *NV = FoldOpIntoPhi(SI))
+ return NV;
if (BinaryOperator::isNot(CondVal)) {
SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));